Comparison of the intestinal secretory response to 5-hydroxytryptamine in the rat jejunum and ileum in-vitro.

A secretory response to 5-hydroxytryptamine (5-HT) is observed throughout the intestinal tract; this investigation has compared the nature of this response in the jejunum and ileum of the rat in-vitro. Different basal electrical activity was observed for jejunal and ileal sheets of rat small intestine. In both intact and stripped preparations the basal short-circuit current (SCC) was greater and the tissue resistance lower in the jejunum than in the ileum. 5-HT caused concentration-dependent increases in SCC in intact and stripped preparations of both regions. EC50 values were similar in the jejunum and ileum, stripped sheets from both regions showing greater sensitivity. In the ileum the maximum increase in SCC induced by 5-HT was similar in intact and stripped sheets, but in the jejunum the response was greater in intact preparations. The jejunal response to 5-HT was reduced in the absence of bicarbonate but unaffected by lack of chloride, whereas the ileal response was inhibited by removal of chloride but unaltered in bicarbonate-free conditions. In intact sheets the tetrodotoxin-sensitive neural component was greater in the jejunum. In stripped sheets a neural component could still be detected in the ileum, but not in the jejunum. There are, therefore, fundamental differences in the way in which the jejunum and ileum respond to 5-HT stimulation--the jejunal response is primarily a result of stimulation of bicarbonate secretion whereas chloride secretion predominates in the ileum. The myenteric plexus appears to play a more prominent role in the jejunum; in the ileum other neural elements also contribute to the response.